Titanium-beryllium-silicon alloy



Oct. 8, 1963 M. K. MCQUILLAN ETAL 3,106,495

TITANIUM-BERYLLIUMSILICON ALLOY Filed May 25, 1959 2 Sheets-Sheet 2 (\i 9 LL BY W ATTORNEY-Y HARDNESS o. P. N7

B" i 495 Patented Get. 8, 1 963 TITANiUM-BERYLLiiJM-SHJCON ALLQY Marion Katharine McQnillan, Birmingham, and Evan William Evans, Halesoweu, England, assignors to imperial Chemical industries Limited, London, England, a corporation of Great Britain Filed May 25, 1959, Ser. No. 815,732 Claims priority, application Great Britain May 30, 1953 2 Claims. (Cl. 148-13) This invention relates to titanium-base alloys.

Although many titanium alloys have been developed having properties which render them suitable as constructional materials, all suffer from the disadvantage that when in sliding contact under load there is a tendency for the sliding surfaces to seize together, i.e. to gall. The provision of a hard surface on titanium is also desirable from the point of view of wear resistance of moving parts. A large number of methods have been developed for overcoming galling, including the formation of a hard surface layer by induction hardening of certain titanium alloys or by impregnating the surface of the metal with hardening elements. In the latter case there is a tendency for the hardened layer to be either metallurgically unstable at elevated temperatures or to be brittle and to spall oi the surface under operating conditions.

In our application Serial No. 795,461, filed February 25, 1959, now U.S. Patent No. 3,007,824, we describe a method of heat-treating a titanium-base alloy containing between 0.6% and 1.2% beryllium, apart from impurities, in which the alloy is heated to a temperature between 820 C. and the upper temperature limit of the betaphase field of the alloy and is then cooled rapidly by quenching in a suitable liquid medium.

We have now found that by modifying the composition of the alloy by the addition of further alloying elements, improvements in the hardening characteristics of the alloy are obtained.

According to this invention, we provide a method of heat-treating a titanium-base alloy containing between 0.5% and 1.0% beryllium and between 0.25% and 2.0% molybdenum and/or 0.25% and 2.0% silicon in which the alloy is heated at a temperature between 875 C. and 1200" C. and is then cooled rapidly by quenching in a suitable liquid medium.

The time for which the alloys are heated at the high temperature is not critical; 5 minutes after the attainment of the required temperature is usually sufiicient.

As a result of this heat-treatment, the alloys are hardcued and strenghtened, particularly at the surface, and the extent to which this eife'ct occurs is independent of the period of time for which the material is held at the required temperature, but is dependent upon the cooling rate from that temperature.

A high rate of cooling, such as by quenching in iced brine or in water, produces a high degree of hardening on the surface. With slower rates of cooling, as by oil quenching, lower hardness of the surface results. In material other than thin sheet, the interior of the metal (hereinafter referred to as the core) remains comparatively soft. In thin sheet, the depth of hardening may be such as to penetrate through the entire thickness of the material, though in most instances the actual hardness of the core will be less than that of the surface.

Alloys in accordance with the invention harden to a greater depth from the surface than is the case with titamum-beryllium binary alloys mentioned above. For example, test-pieces in the form of rod of inch diameter and 2 inches long made from titanium-base alloys containing respectively 0.8% Be, 1% Mo and 0.8% Be, 2% M0, were heated to a temperature of 1000 C. and quenched into iced brine. The hardness of the test-pieces was in excess of 450 Vickers diamond pyramid hardness (V.D.P.H.) throughout the entire cross-section, reaching over 500 V.D.P.H. at the surface of the rod. A similar test-piece made from the binary titanium-beryllium alloy containing 0.8% Be, given a similar heat-treatment hardened on the surface to more than 500 V.D.P.H. but in the centre of the cross-section had a hardness of only 337 V.D.P.H.

The effects of the hardening heat-treatment on ternary alloys containing molybdenum and on a binary titaniumberyllium alloy are compared in Table I in which the V.D.P.H. numbers are given. These values were determined at a depth of 0.05 inch below the original surface in order to avoid the effects of contamination of the surface, which may have occurred during heating. It will be observed that hardening in various degrees can be obtained by air cooling, oil quenching and iced brine quenching.

in Table II are set out hardness values measured at intervals across the cross-sections of inch diameter testpieces of the binary titanium-beryllium alloy and of a ternary alloy containing molybdenum. Although the ternary alloy has been less drastically quenched than the binary alloy, the ternary alloy has hardened to a higher value through the cross-section than the binary alloy in which high hardness values are found only at the surface.

Table III shows hardness values determined on a series of ternary alloys containing the beta stabiliser molybdenum quenched from 1000 C. into iced water. The values were measured near the edge, at the centre and at two intermediate points of a cross-section of a inch diameter rod. It will be seen that an increase in molybdenum content produces an increase in hardness levels throughout the cross-section.

For small articles or articles of thin gauge, in order to produce a suitable hardness gradient between the surface and the core, it may be advantageous to select alloy compositions in which the molybdenum and/or silicon content is in the lower part of the range. articles or articles of heavy gauge may require the alloy composition to be in the upper part of the range.

Heat-treatments carried out after hardening have shown that no appreciable loss of hardness is likely to occur if the hardened alloy is heated in service to temperatures less than 400 C. If the hardened alloys are heated at higher temperatures up to 800 C., the hardness is re duced. Results of heating the hardened alloys at different temperatures, i.e. 400 C. and 600 C. for different periods of time are shown in graphical form in FIGURE 1 of the accompanying drawings. Incidentally, the effect of quenching from two different temperatures is also shown in FIGURE 1 by the hardness values for zero time and it is apparent that a temperature of 1000 C. produces higher surface hardness than a temperature of 875 C.

Silicon has a similar effect to molybdenum in producing higher hardness levels when added to the titaniumberyllium binary alloy. The effect of 'diifercnt amounts of silicon on the hardness values across a rcross-section of inch diameter rod quenched in iced water from Conversely, large,

3 1000 C. is shown in Table IV and these values should be compared with those for the binary alloy in Table II. FIGURE 2 of the accompanying drawings shows the hardness values of the 0.6% silicon ternary alloy of Table IV plotted in graphical form. The pronounced hardness gradient is well demonstrated in FIGURE 2.

Silicon may replace part of the molybdenum, thus making a quaternary alloy. Similar hardness levels and gradients are produced in the quaternary alloys to those of the ternary alloys. A quaternary alloy containing 1% beryllium, 1% molybdenum, 1% silicon in the form of a test-piece having an effective cross-section of /2 inch was heat-treated in accordance with the method of the invention. Hardness measurements gave values of 535 V.D.P.H. near the surface decreasing to 350 V.D.P.H. at the core.

Microstructural examination of the test-pieces showed that the hardened material was confined to the surface layers in the case of the binary alloy, whilst the ternary alloys were hardened throughout the cross-section.

The above ternary and quaternary alloys have moderately high tensile strength of about 50 tons/sq. in. with reasonable ductility, after receiving heat-treatment in accordance with the invention, the actual values depending on the severity of the quench. In the soft condilion, the alloys may be easily worked and the hard surface may then be produced by the heat-treatment herein described.

Table I T able III Hardness (V.D.P.H.) across Mo, 13c, section of inch bar Vt. \Vt. Percent Percent Edge Centre Table IV Hardness (V.D.P.H.) across Section of ineh her Si, Wt. Be, Percent \Vt.

Ier- Edge Centre Edge cent We claim:

and 2.0% of silicon remainder titanium apart from impurities.

2. A method of heat treating a titanium-base alloy 005 INCH BELOW 'IIIE SURFACE Heatedto 875 C. Heated to 1,000 C. Hardness Annealed Composition as forged at 875 C.

and and slow Oil Iced Air Oil Iced rolled cooled quench brine cooled quench brine quench quench ']i-O.8% Be 257 179 207 304 283 341 417 li0.8% lie-1% M0... 285 225 358 437 347 445 515 Ti-08% Be-2% Mon 283 205 206 373 200 323 502 Table II containing between 0.5 and 1.0% beryllium, 0.25-2.0%

DIAB'IOND PYRAMID HARDNESS VALUES MEASURED ACROSS SECTIONS OF THE (Pi-0.8% Be AND Ti-0.8% Bo1% M0 ALLOYS of silicon balance titanium apart from impurities, said method comprising heating said alloy to a temperature between 875 C. and 1200" C. and quenching by rapidly cooling the alloys in a liquid medium.

References Cited in the file of this patent UNITED STATES PATENTS 2,801,167 Crossley et al. July 30, 1957 OTHER REFERENCES Titanium Alloys, Sutcliffe, Metal Treatment and Drop Forging, pages 191-197, April 1954. 

1. AN ARTICLE HAVING A HARD SURFACE AND A CORE SOFTER THAN THE SURFACE MADE FROM A TITANIUM-BASE ALLOY CONTAINING BETWEEN 0.5 AND 1.0% BERYLLIUM, BETWEEN 0.25 AND 2.0% OF SILICON REMAINDER TITANIUM APART FROM IMPURITIES. 